Apple Monitor III General Maintenance

Monitor III on an Apple III (Benoît Prieur, Wikimedia Commons, CC0)

Care, opening and the one internal adjustment on record for the Apple Monitor III. Apple's dealers exchanged faulty units without repairing them, so the service details here come from Apple's exchange procedure, the owner's manual and Sams's ComputerFacts for model A3M0039.

Read CRT Discharge Procedure before opening the case.

Glare filter

The microporous glare filter in front of the screen is made of nylon filaments and tears easily. Wipe it occasionally with the cleaning cloth supplied with the monitor. For a deeper clean, rub it gently with a clean lint-free cloth dampened with a little isopropyl alcohol; this can be done with the filter in place. Apple sent anything harder to remove to a dealer, who would take the filter out and clean it in isopropyl alcohol or fit a new one.

General care

Clean the cabinet with a damp cloth, with the monitor unplugged. Keep the ventilation openings clear, including the ones in the bottom, so do not stand the monitor on a soft surface. Keep it away from damp, dust, heat and direct sunlight, and unplug it when it will not be used for a long time. Lift it by the hand grip at the back, with your hand all the way into the opening.

Before connecting a monitor of unknown history, check that its voltage marking matches the supply: the 117 V models (A3M0006, A3M0039) and the 230 V model (A3M0024) are different units.

Opening the case

Apple's exchange procedure removes the rear cover as follows.

1. Switch off and unplug the mains lead.
2. Lay the monitor face down on a soft, protective surface.
3. Remove the two Phillips screws from the bottom of the chassis frame, then lift the rear cover off, feeding the line cord through its opening.
4. With the cover off, do not touch the yoke wires, the anode connector, the anode wire or the flyback transformer.
5. To refit, feed the line cord through the opening, lower the cover onto the chassis, and replace the two screws.

Apple's safety rules for this procedure: remove rings, watches and other jewellery, wear safety goggles, and keep the power off unless a live adjustment requires it, because parts of the chassis are live when the monitor is powered. Discharge the anode before touching anything inside.

B+ adjustment

Sams gives one internal adjustment for model A3M0039: connect a DC voltmeter to the collector of the voltage regulator transistor Q901 and set the B+ control R903 for 11.6 V.

The other controls, from Sams's parts list, are contrast R215 (500 Ω), brightness R264 (500 kΩ), vertical hold R604 (50 kΩ), vertical height R606 (10 kΩ), vertical linearity R607 (5 kΩ), horizontal hold R707 (50 kΩ), sub-horizontal hold R709 (2 kΩ), focus R751 (2 MΩ) and B+ R903 (1 kΩ).

Fusible resistors and special parts

Sams's list of parts not normally stocked by distributors includes the fusible resistors R301 (2 Ω 1/4 W) and R712 (10 Ω 1/4 W), R258 (1200 Ω 3 W metal oxide), R905 (27 Ω 5 W wirewound), C703 (100 pF NPO 50 V) and the non-polarised electrolytic C712 (6.8 µF 25 V).

Capacitors

Sams lists only C712 among the electrolytics; the other capacitor values are on the Sams schematic and on Apple's schematic in the owner's manual. Sams names C901 and C909 in the power supply and C604-C608, C610 and C712 in the deflection circuits as parts to check. General failure signs are on Capacitor Failure Symptoms.

Related pages

• Apple Monitor III
• Apple Monitor III Troubleshooting Guide
• Apple Monitor III Documentation